1. Field of the Invention
The present invention relates to a formation method of a pattern, and more particularly to a formation method of a precise pattern in a good configuration.
2. Description of Related Art
As semiconductor devices are more highly integrated and developed higher performance, there is an increasing demand for precise patterns for formation of wirings or the like and it is becoming important to form patterns of high precision through a photolithography technique. With reference to FIGS. 2(a) to 2(c), a formation method of a pattern on a semiconductor substrate through a conventional photolithography technique will be explained.
First, as shown in FIG. 2(a), a photoresist layer 2 is formed on a semiconductor substrate 1 by a coating method. Next, as shown in FIG. 2(b), the photoresist layer 2 is exposed to exposure light such as ultraviolet light and an electron beam (EB) via a mask 3 to form an image of a desired pattern on the photoresist layer 2. Subsequently, the photoresist layer 2 is developed with a developer such as an alkaline aqueous solution to partially dissolve and partially make remain the photoresist layer 2. Thus, a pattern 4 made of a resist is formed.
Here, a resist of which an exposed portion is dissolved by development is referred to as a positive resist whereas a resist of which the exposed portion is made to remain by development is referred to as a negative resist. In photolithography techniques using wavelengths of a g-beam and an i-beam, normally used is the positive resist because of its good performance (concerning resolution, depth of focus and the like).
Further, a formation method of a resist pattern with a higher resolution is disclosed in Japanese Unexamined Patent Publication No. HEI 9(1997)-190959. This method is intended to form a narrow space pattern or a contact hole pattern, utilizing the dependence of resolution of the resist pattern on a configuration of the pattern itself.
The method disclosed in the above-mentioned publication will be briefly explained with reference to FIGS. 3(a) to 3(c).
First, on a semiconductor substrate 11 is formed a pattern such as a densely formed trace pattern, an isolated trace pattern or a pillar pattern having a comparatively high resolution. In FIG. 3(a), a pillar pattern 12 is formed as an example of the pattern. The formation of the above pattern utilizes the fact that a pattern such as the densely formed trace pattern, the isolated trace pattern or the pillar pattern in which a portion remaining after the development forms a pattern shows a higher resolution than a pattern such as a contact hole pattern or an isolated-space pattern in which a portion dissolved after the development forms a pattern. Subsequently, as shown in FIG. 3(b), a negative photoresist layer 13 is formed on the entire surface of the substrate. Then, only the pillar pattern 12 is removed by whole light exposure and development. Thus, a hole pattern 14 can be obtained finally as shown in FIG. 3(c).
In order to realize scale reduction of semiconductor devices, it is required to improve the resolution of a resist layer and set various conditions in the formation of a pattern for enlarging clearance for defocus (depth of focus).
A pillar pattern employed mainly as a mask for ion implantation is especially required to be formed with high precision because its configuration is greatly influential in characteristics of transistors. As scale reduction of semiconductor devices is progressing, it is becoming necessary to control the configuration of a resist pattern precisely.
In the cases where a pattern such as the pillar pattern is formed using the positive resist as employed in the above-mentioned conventional art, after the developing, the pattern is liable to have a gently-sloping mountain-like taper as shown in FIGS. 4(b-1) and (b-2) under the influence of light diffracted from the outside of the mask 3 at the exposure to light as shown in FIGS. 4(a-1) and 4(a-2).
As mentioned in the above publication, indeed the pillar pattern offers a relatively higher resolution than the hole pattern. However, the difference in resolution between the pillar and hole patterns is only 0.05 xcexcm in the case of a design rule of 0.35 xcexcm using exposure light of an i-beam and a positive resist. As to the clearance for defocus (depth of focus), that for the formation of the pillar pattern is extremely smaller than that for the formation of the hole pattern (see Table 1). This phenomenon becomes more apparent as intended pattern dimension becomes more minute, and it is difficult to form the pillar pattern while keeping a stable depth of focus when the pattern dimension is on the order of a quarter micron or less. In Table 1, the depth of focus means the range of focus in which a pattern is in error of xc2x10.05 xcexcm and is free from defects (failure in opening configuration, short circuit, break of wirings, loss of resist film height or the like).
The present invention provides a first formation method of a pattern comprising the steps of: forming a photoresist layer of a positive type on a substrate; exposing to light and developing the photoresist layer using an inversion mask having an opening at a site at which a pattern is desired to be formed finally, thereby forming an opening portion in the photoresist layer to expose the substrate at the site; applying a non-photosensitive organic film on an entire surface of the substrate including the photoresist layer, so that the non-photosensitive organic film is embedded in the opening portion; etching back an entire surface of the non-photosensitive organic film on the photoresist layer until the photoresist layer is exposed; and exposing to light and developing an entire surface of the photoresist layer to remove the photoresist layer, thereby obtaining the non-photosensitive organic film having the desired pattern.
Further, the present invention provides a second formation method of a pattern comprising the steps of: forming a first photoresist layer of a positive type on a substrate; performing a first exposure to light and development by exposure light having a predetermined wavelength using a inversion mask having an opening at a site at which a pattern is desired to be formed finally, thereby forming an opening portion in the first photoresist layer to expose the substrate at the site; applying a second photoresist layer on an entire surface of the substrate including the first photoresist layer, so that the second photoresist layer is embedded in the opening portion; etching back an entire surface of the second photoresist layer on the first photoresist layer until the first photoresist layer is exposed; and exposing to light and developing an entire surface of the first photoresist layer and an entire surface of the second photoresist layer by exposure light having the same wavelength as that of the exposure light used in the formation of the opening portion, to remove the first photosensitive layer, thereby obtaining the second photoresist layer with the desired pattern.
These and other objects of the present application will become more readily apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.